1. Field of the Invention
The present invention relates to the field of mass storage devices for storage and retrieval of information, such as may be utilized, inter alia, by computer systems for archival storage of digital data, for storage and retrieval of document images and for storage of video images or sound recordings; in particular, the present invention relates to the field of optical storage systems, preferably using flexible media such as optical tape.
2. Description of Related Art
Numerous prior art systems are available for the storage and retrieval of information. In each of these systems, certain objectives are clear. It is important to provide for storage and retrieval of information at high speed while maintaining the cost of the storage media and associated hardware at a low cost.
One example of such a storage media is magnetic tape which is typically used for archival storage of information on computer systems and the like. As a particular example magnetic tapes for use with the IBM Model 3480 tape drive are capable of storing 200 megabytes of information. The 3480 tape drive is capable of running the tape from end-to-end in approximately 45 seconds and allows for an average access time of 15 seconds and a standard input/output data rate of 3.0 megabytes per second.
Presently, demand for data storage and retrieval capability is increasing and this increase in demand is expected to escalate in the future. There are numerous reasons for the expected increase in demand for data storage capacity, such as the need to store bit-mapped images of documents, etc. Therefore, it is desired, as one aspect of the present invention to provide a storage and backup system which provides for increased storage capacity, decreased retrieval times and low cost.
One emerging technology useful for the storage and retrieval of information is optical storage systems. Such systems allow for storage and retrieval of information on a medium through use of a light source. A well-known example of an optical storage system is an optical disk. Optical disks are utilized in a variety of functions such as recording of digitally encoded music, permanent storage of data for computer systems, etc.
Flexible optical tape, as opposed to optical disk, has recently entered the market. Optical tape allows for storage of information on optical media with virtually limitless capacity. Non-erasable write once read many (WORM) optical tape is currently available from ICI Imagedata, P.O. Box 6, Shire Park Bessemer Road, Welwyn Garden City, Herts AL7 1HD, ENGLAND. The particular tape manufactured by ICI is available in 35 mm width allowing data to be laser written in a center section at 30 megabytes per square inch (roughly the equivalent in a square inch of medium to 100 standard 51/4 inch double-sided double density floppy disks). Erasable optical tape is expected to be made available in the future. The present invention may work with either erasable or WORM recording media.
Data recording/retrieval systems are known which utilize a light source(s) for reading/writing. For example, U.S. Pat. No. 3,874,621 Blair et al., describes a system in which a continuous wave gas laser is focused at a spot on film. The continuous laser is modulated by a modulator and the light beam is directed to the film through a mirror system.
U.S. Pat. No. 4,168,506 Corsover discloses a film guide for an optical scanner including a modulator and laser source, a first mirror and a second rotating mirror, a lens assembly and a film guide for passage of a recording medium.
More recently, U.S. Pat. No. 4,567,585 Gelbart disclosed an optical tape recording system which utilizes the linear motion of a slide to record data across a slowly moving optical tape. Data is recorded on the tape by modulating the output of a laser in accordance with the data and focussing the modulated light onto the tape.
U.S. Pat. No. 4,577,932 Gelbart describes a laser system in which a single pulse from a light source generates a multi-spot image of a data pattern on a medium through use of an acousto-optic modulator. This reference is typical of prior art systems in which a data signal is used as input to a modulator and a synchronization signal is used as input to a light source.
U.S. Pat. No. 4,743,091 Gelbart describes a system in which a two-dimensional array of discrete laser diodes is utilized to write information on the surface of a light sensitive material.
Finally, U.S. Pat. No. 4,815,067 Webster et al. describes a helically scanned optical tape recording and replay system which utilizes a rotating drum with a galvanometer mirror for controlling the tracking of a number of write and read light beams during recording and replay.
It is desired, among other objects of the present invention, to develop an improved system for reading and/or writing to optical recording media, preferably optical tape.
It is further an object of the present invention to develop a system for reading and/or writing to optical recording media comprising improved means for scanning a radiant energy source onto the media.
It is still further an object of the present invention to develop an optical recording/writing system having improved capability of determining positioning for reading and/or writing to an optical recording media.
It is another object of the present invention to develop an optical recording/writing system having improved capability for focussing of a radiant energy beam on an optical recording media.
These and other objects of the present invention will be appreciated by one of ordinary skill in the art with reference to the below recited Detailed Description of the Preferred Embodiments and the accompanying figures.